Yttrium-hydrogen isotope compositions for radiochemical reactions

ABSTRACT

Compositions for radiochemical reactions including yttrium deuterides and tritides and solutions of deuterium and tritium in yttrium alloys with titanium and/or zirconium.

United States Patent 1m nu 3,716,491

Yannopoulos et al. I 1 Feb, I3, 1973 YTTRIUM-HYDROGEN ISOTOPE [56] References Cited COMPOSITIONS FOR RADIOCHEMICAL REACTIONS UNITED STATES PATENTS 3 183 356 5/1965 Cherubini ..250/84.5 [76] Inventors: Lympenos N. Yannopoulos, 309 2 4 dg A en e, pt. E Pitt 3,320, 2 5/1967 St. John ..250/8 .5 sburgh, Pa. 15218; Sven A. Jansson, OTHER PUBLICATIONS 109 Glenfield Drive; Earl A. Gulbransen, 63 Hathaway Court, both of Pittsburgh, Pa. 15235 [22] Filed: July 9, 1969 Prima Examiner-Leland A. Sebastian "y 1 pp No 840 162 Attorney-F. Shapoe and Lee R Johns Detaint, Nucl. Sci. Abstract, 1968, 22(17), 37244, pp. 3792 to 3793.

57 ABSTRACT [52] gg Compositions for radiochemical reactions including In C (369k 0 g yttrium deuterides and tritides and solutions of deuterium and tritium in yttrium alloys with titanium [58] Field of Search ..l76/10; 250/845; 313/61 S; and/Or Zirconium 117/62, 106 R; 75/122.5;'252/301.l R

6 Claims, 2 Drawing Figures (X PARTICLES AND NEUTRONS DEUTE RON BEAM PAn-imanrrm w 3.716.491

SHEET 101- 2 l2 A A A '0 v v v I i C- EQUILIBIUM HYDROGEN PRESSURE FOR Ti-H AND Y-H SYSTEMS AT (H/M)=|.O FOR TiH AND AFOR YH PAIENIEU FEB 1 3191s SHEET 2 BF 2 DEUTERON BEAM 20 YTTRIUM-HYDROGEN ISOTOPE COMPOSITIONS FOR RADIOCHEMICAL REACTIONS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to hydrogen isotopes in yttrium base alloys of titanium and/or zirconium, and more particularly, it pertains to a target for radiochemical reactions of tritium or deuterium absorbed in yttrium with or without titanium and/or zirconium.

2. Description of the Prior Art Titanium and zirconium deuterides and tritides have been used as targets for radiochemical reactions as sources for electrons and for deuterium and radioactive tritium gas, such as reported in a Russian Journal, Pribori l Tekhnika US. Pat. No. 5, 1962, page 38. With titanium and zirconium deuterides and tritides, however, the retainment of gas has been a problem during their preparation as well as during operation of targets at a high energy level. As sources of gases and of electrons therefor, deuterides and tritides of titanium and zirconium have been less stable than was previously anticipated and have required the use of supplementary water cooling devices where elevated temperatures of operation are involved.

SUMMARY OF THE INVENTION It has been found in accordance with this invention that deuterides and tritides of yttrium alloys with titanium and zirconium have high stability and are useful as materials for retaining and for releasing deuterium or tritium gas in a controlled manner as needed. The retainment and release of the deuterium or of the radioactive tritium can be controlled by regulation of the temperature of the yttrium alloy source.

Accordingly, it is an object of this invention to provide yttrium-hydrogen isotope compositions for more efficient and convenient radioactive determinations.

It is another object of this invention to provide yttrium-hydrogen isotope compositions as targets for radiochemical reactions.

It is another object of this invention to provide yttrium-hydrogen isotope compositions as sources for gases and electrons for controlled sparks.

It is another object of this invention to provide yttrium-hydrogen isotope compositions having higher stability than deuterides and tritides of prior known metals.

Finally, it is an object of this invention to satisfy the foregoing objects desiderata in an expedient manner.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention reference is made to the drawings, in which:

FIG. 1 is a graph in which the equilibrium hydrogen pressures for Ti-H and Y-H systems are compared over the same temperature range;

FIG. 2 is a partial vertical sectional view through a neutron target mounted in a holder within a neutron accelerator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Yttrium dissolves hydrogen in solid solution to an H/Y atom ratio of about 0.40 at 600C. Higher hydrogen concentrations correspond to hydride formation. The hydrogen equilibrium pressure at 400C is lower than 10 7 torr for the two phase system as extrapolated from experimental data and is expressed in the formula:

The deuterium and tritium equilibrium pressures over the two phase field [yttrium and deuterium (or tritium) and the deficient yttrium dideuteride (or ditritide) in equilibrium] are greater than the corresponding hydrogen pressure value by a factor of 2 to 3, but still close to 10 torr for temperatures of up to about 400C.

In FIG. 1 a comparison of the equilibrium hydrogen pressures is shown for Ti-H systems where the atom ratio, HIM, is 1.0. As shown in FIG. 1, for a given temperature the titanium hydrogen system is less stable than the yttrium-hydrogen, Y-I-I, system. The horizon tal dotted line at a hydrogen pressure of 2 X 10 torr indicates the point at which hydrogen begins to be present in amounts sufficient to create problems. The temperature at that pressure for the Ti-H system is about 250C, whereas for the Y-H system the corresponding temperature is about 575C. The ZrI-I system is only slightly more stable than the Ti-H system. This indicates that the Y-H system is substantially more stable and the yttrium-hydrogen system can therefore be operated at higher temperatures before excessive hydrogen is evolved than hydrogen systems with such metals as titanium and zirconium.

The equilibrium hydrogen pressures for the systems of Ti-H and Y-I-I at the atomic ratio of I-I/M being 1.0, are also listed as shown in the Table.

[ Pln,

TABLE EQUILIBRIUM HYDROGEN PRESSURES (PIHZ, torr) Temperature (C) TiH YH Data for Ti-H system from extrapolation of plot in Proc. Roy. Soc. (London) A204,309 (1950) and Y-H from extrapolation from J. Phys. Chem. 69, 2510 (1965).

The values in the Table are shown in the graph of FIG. 1.

One of the applications of this invention utilizes yttrium alloys for the retention of tritium in the production of neutrons. The higher stability of yttrium ditritide, YT over that of ZrT or TiT enables the use of tritides of yttrium metal and yttrium alloys as neutron targets with advantageous results.

In FIG. 2, a portion of a neutron accelerator is generally indicated at 10. It includes a housing 12 having a branch portion 14 extending from one side thereof. The accelerator 10 also includes a neutron target holder 16 for supporting a target 18 in a conventional manner within the housing 12. Thus, as a deuteron beam, indicated by the arrow 20, is directed to the surface of the target 18, under conditions to be described hereinbelow, alpha particles and neutrons are emitted from the target in a direction indicated by the arrow 22.

The target 18 consists of a substrate 24 and a top coating 26. The substrate is composed of a metal such as tungsten, stainless steel, or copper. The coating 26 is a thin film composed of yttrium base alloys, with some titanium and/or zirconium being present if desired, together with a hydrogen isotope gas such as deuterium or tritium. The target 18 is prepared generally in accordance with the following steps:

1. Providing a substrate of suitable diameter such as 2.5 centimeters and having a thickness of about 2 millimeters which substrate is preferably composed of tungsten;

2. Depositing yttrium-base alloy (with titatium and/or zirconium) by vapor deposition to a uniform thickness of from about 10 ug/cm where the target is to be used as a neutron target, and to a thickness of from about 3 to 10 microns where the target is to be used in controlled spark devices;

3. Charging the resulting coating of yttrium base alloy with tritium gas to a selected concentration, for example, in a volume sufficient to give YT while the coating is at a temperature ranging from about 500 to 950C, preferably 600C; and

4. Cooling the assembly of the substrate and coating to room temperature within an enclosing chamber whereby all of the tritium in the chamber is absorbed by the yttrium coating and the coating has essentially the formula YT.

Thereafter, the target 18 is placed in the neutron accelerator 10 which is then evacuated to a pressure range of about 10 torr. The accelerator with the target 18 is then heated under vacuum to a temperature ranging from about 300 to 400C for the purpose of removing all absorbed gaseous impurities, such as carbon dioxide, oxygen, nitrogen, water vapor. The target is then bombarded with a deuteron beam 20 as shown by the arrows in FIG. 2.

Generally, when tritium is bombarded with deuteriurn, it produces alpha particles (He) and neutrons in accordance with the following formula:

Tritium gas is absorbed in the yttrium coating 26 where it is firmly retained as the hydride even at high vacuum at temperatures of up to 450C. Heretofore, with target constructions having a coating 26 composed of zirconium or titanium, tritium began to escape from the coating with increasing vapor pressure as the bombardment temperature increased toward the range of 220 to 250C. A cooling system for the target was necessary to maintain stability. Where, however, the coating 26 is composed of yttrium base alloy Le. a minimum of 50 w/o yttrium, the tritium present therein does not escape under these conditions and the target can be heated to a temperature range of from about 300 to 450C without losing tritium gas.

Deposition techniques for depositing yttrium alloys of zirconium and titanium include vaporization, sputtering, and vapor deposition from volatile halides. After the coating or layer of yttrium alloy is applied,

the layer is charged with the hydrogen isotope deuterium or tritium by heating the metal to a temperature of from 500 to 950 in an atmosphere of the hydrogen isotope. When allowed to cool, the metal absorbs more of the hydrogen isotope. When properly charged, substantially all of the deuterium or tritium will be absorbed by the yttrium. The absorption is promoted by making sure that the metal is initially well outgassed and a sufficiently good vacuum is maintained at the critical stages of operation to prevent absorption of other contaminating gases. The presence of or the absorption of certain gases such as nitrogen or oxygen may prevent the subsequent absorption of hydrogen. Where the target is very thin, the contamination difficulties are especially pronounced. For that reason pretreatment in a vacuum of better than 10% mm Hg while at maximum temperature is recommended.

Where tungsten is used as a substrate, it should be previously outgassed at temperatures of about 2,000C. Likewise, yttrium should be outgassed before the evaporation or melting operation is begun. Outgassing of the substrate enhances adhesion of the yttrium coating and heating of the substrate during bombardment or deposition of the yttrium at about 400C improves adhesion.

Yttrium ditritide targets have two advantages over zirconium and titanium ditritide targets namely, l the targets can be baked out at 300 to 450C without losing any significant amount of the tritium gas, and (2) larger beam currents can be used without elaborate cooling techniques.

Another application of yttrium ditritide is in controlled spark devices. Present designs using tritium gas at low concentrations to furnish electrons for initiating the spark when the voltage is applied to the gas.

The device of the present invention incorporates the active tritium gas in a thin layer of yttrium base alloy of zirconium and titanium on the surface of the electrodes. The higher stability of the Y-l-l system will allow smaller quantities of tritium to be used. This will minimize radiation hazards.

Although the best known embodiment of the invention has been described in detail, it is understood that the invention is not limited thereto or thereby.

What is claimed is: i

l. A target useful as a bombardable source for electrons and alpha particles comprising a hydrogen isotope selected from at least one of the group consisting of deuterium and tritium combined with a metal selected from the group consisting of yttrium-base titanium alloy, yttrium-base zirconium alloy, and alloys of yttrium, titanium and zirconium.

2. The target of claim 1 wherein the metal is an alloy of yttrium and titanium.

3. The target of claim 1 which consists of deuterium absorbed in an alloy of yttrium and zirconium.

4. The target of claim 1 which consists of tritium absorbed in an alloy of yttrium, zirconium, and titanium.

5. A target for radiochemical reactions consisting of a composition ofa hydrogen isotope in a metal selected from a group consisting of yttrium-base alloy with titanium, yttrium-base alloy with zirconium, and yttrium base alloy with titanium and zirconium, the composition being a minimum of 50 w/o of yttrium retained as a separate phase in the matrix, with the balance being zirconium or titanium.

6. A target comprising tritium with a metal selected from a group consisting of yttrium-base titanium alloy, yttrium-base zirconium alloy, and alloys of yttrium, titanium and zirconium. 

1. A target useful as a bombardable source for electrons and alpha particles comprising a hydrogen isotope selected from at least one of the group consisting of deuterium and tritium combined with a metal selected from the group consisting of yttrium-base titanium alloy, yttrium-base zirconium alloy, and alloys of yttrium, titanium and zirconium.
 2. The target of claim 1 wherein the metal is an alloy of yttrium and titanium.
 3. The target of claim 1 which consists of deuterium absorbed in an alloy of yttrium and zirconium.
 4. The target of claim 1 which consists of tritium absorbed in an alloy of yttrium, zirconium, and titanium.
 5. A target for radiochemical reactions consisting of a composition of a hydrogen isotope in a metal selected from a group consisting of yttrium-base alloy with titanium, yttrium-base alloy with zirconium, and yttrium base alloy with titanium and zirconium, the composition being a minimum of 50 w/o of yttrium retained as a separate phase in the matrix, with the balance being zirconium or titanium. 